The present invention relates to a manual tensioner with a cutter that may be used to apply a non-metallic strap around a load and to cut the strap from a strap supply.
Straps are wrapped around loose objects, such as lumber, to bind the objects together. Straps are also wrapped around boxes and other items to package and secure the boxes and items together. Straps of different materials are often used to tighten different types of loads. For example, plastic straps are often used to tighten lumber loads and boxes. Tensioners are used to tighten or tension the straps around the load. Further, there are tensioners designed for metallic straps and others for plastic or non-metallic straps. A hand-held or manual tensioner is typically used when a load is to be tightened in the field, such as the one shown in FIG. 1.
Non-metallic hand held tensioners of the art are able to tighten the strap around the load, but they suffer from many shortcomings. For example, after wrapping the strap around the load, it is desirable to manually pull the strap to remove any excess slack. This typically reduces the time and number of steps required to complete a strapping operation, i.e., to tighten the strap around the load. However, prior art tensioners used with non-metallic straps incorporate gear box assemblies that either did not allow for manual slack reduction or incorporated very cumbersome slack reduction mechanisms. In other words, after the strap is wrapped around the load and fed into the tensioner, the user either cannot pull an end of the strap to manually remove excess slack or cannot remove excess slack without exerting great effort.
In addition, other tensioners of the art incorporate a double strap or a strap-on-strap loading mechanism. A first portion of the strap is held in place by a gripper, and a down stream portion of the strap is wrapped around the load and positioned over the first portion. This forms a top strap layer, and the portion of the strap underneath the top layer is the bottom layer. A feed wheel pushes down over the top layer.
A lever 12 of the tensioner 10 (FIG. 1) is rotated downward to actuate the gear system of the tensioner and begin the tightening or tensioning process. These tensioners incorporate a single ratchet gear system where the ratchet gear is rotatably mounted to the lever 12. The feed wheel is coupled to the ratchet gear by a shaft so that, when the lever is pushed down, the ratchet gear and the feed wheel turn clockwise. The feed wheel is in frictional contact with and pulls and/or tensions the strap around the load when it rotates. Specifically, the strap is tensioned or pulled toward a proximal end 14 of the tensioner 10, away from a distal 16 end of the lever 12, which extends toward a distal end 18 of the tensioner 10.
In sum, the feed wheel rotates clockwise and the strap is tensioned away from a distal end of the lever and tensioner 16, 18. This causes a force distribution on the tensioner 10 and strap that tends to cause the feed wheel assembly to “open up.” In other words, when the strap is subject to high tension forces and the lever 12 is pushed down, the tensioner tends to tilt upward, causing the feed wheel to apply a weaker downward force on the strap. As a result, the strap may slip from the feed wheel and/or the feed wheel may mill or shear top portions of the plastic strap off. To counteract the opening-up phenomenon, the user must exert additional downward force on the tensioner 10 to prevent strap slippage and/or milling. Applying the additional downward force will prematurely tire the user.
To alleviate these problems, a different tensioner adopted a single strap design where a first end of a plastic strap was placed on a gripper having a bottom surface and a pivoting top surface. The first end of the plastic strap is placed on the bottom surface, and the top surface is pivoted and forced down over the bottom surface by way of a spring mechanism.
A downstream portion of the strap is wrapped around the load and slotted into a windlass. Specifically, the lever is attached to a ratchet gear, and the ratchet gear is coupled to the windlass by a shaft. When the lever is pushed down, the ratchet gear rotates, causing both the shaft and the windlass to rotate. The strap is wound around the windlass.
The gripper does not “energize” or clamp into the strap as well as a feed wheel when the strap is very tight or subject to high tensile forces. As a result, the strap may slip within the gripper and/or mill or be sheared by the gripper. Because the gripper comprises two different surfaces that are pressed upon each other, the top surface may not lie evenly flat over the bottom surface, causing one row of gripper teeth to be in closer contact with the strap than the other row. This also causes milling.
Further, tensioners using windlasses require greater forces to tighten the strap around the load, the tighter the strap is wound around the load. The reason is that the mechanical advantage of the tensioner decreases as the radius from the center of the windlass to the outermost strap wrapped around the windlass increases. As the strap is tightened around the load, additional strap revolutions are wound up around the windlass, causing the radius from the windlass center to the outermost strap to increase. A decreased mechanical advantage is the result.
After the strap is tensioned around the load, a separate sealing tool is used to crimp a sealing clip around the bottom and top strap layers to seal the layers together. The clips often include a body portion about as wide as the strap and two arms that depend from the edges of the body. The body of the seal is positioned atop the strap and, ideally, the arms of the seal should depend below the bottom strap. In this manner, the sealing tool can crimp the arms together below the bottom strap. However, the bottom and top strap layers often lay flush against the load, causing the arms of the sealing clip to abut the edges of the strap layers instead of depending below them. As a result, a user often inadvertently crushes the edges of the strap when crimping the arms of the clip.
One end of the plastic strap is typically cut after the seal is applied. Many known tensioners include cutters to cut the strap, but the cutters are difficult to use. Some cutters require the user to completely remove the tensioner from the sealed strap, and others increase the risk of inadvertently cutting the strap before the seal is applied. For example, some tensioners incorporate a cutter that is positioned toward a distal end of the tensioner and is actuated when the lever is pushed down beyond a breaking point. The problem is that the lever is also pushed down to tighten or tension the strap around the load, and a great deal of force must be applied to the lever to tighten the strap. Thus, the lever can be inadvertently pushed down beyond the breaking point before the seal is applied, causing the blade to prematurely cut the strap. This would require a user to start the strapping process again.
Tensioners of the art also were manufactured from one piece gearboxes that made disassembly very cumbersome and difficult. In addition, the gear box assembly incorporated springs that acted against various gearbox components, also making disassembly and reassembly of the gear box difficult.
As a result, there still exists a need for an apparatus and method for an improved manual tensioner that can be used to tighten a non-metallic strap around a load.